I've found this one just naturally completes when a celebrity sim is out in public enough times. It just seems to happen at random, the action/animation is very short, and you don't really get a notification that it's occurred. It's not so much that fans ask, they just seem to pose somewhere in proximity to you and snap a selfie with you in the background. That part of the aspiration was over literally before I knew it, as I didn't notice the counter ticking on it until after a celebrity sim's first meet and greet was over.
